There is a need for the normal playback speed of disk drives, in particular, Compact Disk (CD) or Digital Versatile Disk (DVD) drives, to be readily upgraded for use with faster disk drives. There are two types of modulation used to read to or write data from a disk: Constant Linear Velocity (CLV) modulation and Constant Angular Velocity (CAV) modulation.
CLV provides a way of reading and writing data to disk that uses a single track in a continuous spiral from the center of the disk to the circumference, instead of several concentric circles as with CAV modulation. Each sector of a CLV disk is the same physical size and the disk drive continuously varies the rate at which the disk spins so that as the read/write head moves from the center of the disk, the disk slows down. In other words, the disk rotation speed necessarily varies with the radius of the disk so that the read data rate can be held constant. The faster that the disk is able to spin, the shorter the access times needed since the rate of change is a rate dependent on a faster overall rotating speed. Since the CLV disks have retained the same diameter for the sake of uniformity, increasing the overall speed of rotation means that the data on the data-efficient CLV modulated disks will need to be accessed in correspondingly shorter times and the read rate adjusted to be correspondingly faster. CLV also provides for more data storage on the disk than drives using CAV modulation.
CAV causes the disk to rotate at a constant speed, with the number of bits in each concentric track being the same. Because the inner tracks are smaller in diameter than the outer tracks, the density on the outer tracks is less than optimum. Thus the problem of data access is not as critical with the less data-efficient CAV disks as compared to CLV. The CAV disk does permit fast data retrieval and is well suited to storing high-resolution photos or video. The CAV disk can be designed to operate with an access time suited to the most critical inner track where data density is the greatest with no concern for holding the read rate constant as with the variable rotation speeds of CLV disks. However, as drive rotation speeds increase, even the access times for reading data on the inner tracks of the CAV disks will become a critical design parameter. For example, when the track jump commands enable the actuator to move from inner tracks to outer tracks, the actuator moves faster than the disk rotation speed and the read rate changes as a function of radius thus engendering a requirement for faster access and seek times to accommodate this change.
The codes used to program the disk drives (either CD or DVD) are "DC-Free" codes, i.e.; the long-term average duty cycle is 50%. CDs use an eight-to-fourteen bit code termed EFM while DVDs use an eight-to-sixteen bit code termed EFM Plus. The EFM system maps eight user bits into fourteen channel bits, while using only a subset of all possible 14-bit words. The EFM Plus system maps eight user bits into 16 channel bits while using a subset of all possible 16-bit words.
For CD drives, only the words that satisfy the run length constraints of no fewer than three channel bits and no more than 11 channel bits between transitions are used. The code is called the (2,10) Run Length Limited code. This yields a minimum of two zeroes between the marks and a maximum of ten zeroes between the marks. As an example, 100100 is written as 3T/3T and yields the maximum frequency while 1000000000010000000000 is written as 11T/11T and yields the minimum frequency. The encoder appends three additional channel bits (to the maximum of 11) for charge control. This forces the duty cycle to 50%. The short sector in the CD Read-Only-Memory (ROM) drive consists of 588 channel code bits and has only one synchronization pattern: 11T/11T. There is one synchronization pattern in every sector (588T) and it is not treated as normal data. The data rate of incoming data can be determined by calculating the duration of this incoming 11T/11T-synchronization pattern. The 11T pattern is the longest signal pattern for a CD drive but there can be no 11T/11T combination in the data stream for a conventional CD-ROM's drive.
For DVD drives, only words that satisfy the run length constraints of no fewer that 3 channel bits, and no more than 11 channel bits, between transitions are used, i.e., the same (2,10) Run Length Limited code as for the CD drives. However, there are four states of the conversion table and each state is selected by a DC component suppress control (DCSC) algorithm, permitting the suppression of the DC component of each. The short sector in the DVD-ROM drive consists of 1488 channel code bits with only one synchronization pattern: 14T/4T. There is one synchronization pattern in every sector (1488T) and it is not treated as normal data. The data rate of incoming data can be determined by calculating the duration of this incoming 14T-synchronization pattern. The 14T pattern is the longest signal pattern for a DVD's drive but there can be no 14T/4T combination in the data stream (the EFM Plus Modulation rule identifies it as violated code) for a DVD-ROM's drive. The present invention provides a solution by significantly increasing the PLL's (or PLL equivalent's) capture range.
DVD-ROM drives use a Non-Return-to-Zero (NRZ) format. In EFM Plus code, the signals are inverted at the center of each "1" in the data stream.
Conventional systems use the following process to increase the capture range of the PLL (thus reducing seek/access time):
a. The synchronization pattern is detected as the T.sub.max pattern and the clock's counter is set to count at least twice the rate of the channel code at the maximum disk speed associated with the VCO synchronization clock of the PLL. PA1 b. Upon detection of the T.sub.max pattern, the counter data is transferred to a microprocessor and the data read/write speed is calculated. PA1 c. The calculated speed is reloaded to the VCO synchronization clock and the T.sub.max pattern is compared to the read/write data rate. PA1 d. If the VCO's frequency is not synchronized with the read/write data rate, a "kick pulse" is generated by the microprocessor to adjust the frequency of the VCO. PA1 a. T.sub.max Detection. The Time Base Generator (TBG) VCO's clock is used to find the longest mark and the TBGVCO's clock frequency is used for any frequencies higher than the target read/write data rate. The longest mark is the synchronization mark. In DVD drives, the 14T pattern is used as the synchronization mark. This 14T pattern is the "violated code" of EFM Plus that occurs every 1488 bits in the short frame length. The T.sub.max window is opened approximately six to ten times during the short frame length. The maximum count value encountered during this period is stored in the T.sub.max register. PA1 b. In the synchronization detection step, the data synchronizer voltage controlled oscillator (DSVCO) and the TBGVCO's frequency are the same, with the TBGVCO locked to the DSVCO. During the synchronization step, the DSVCO's frequency is changed to the proportional frequency, i.e., 14/T.sub.max. Unlike conventional systems using PLLs, the proportional frequency is generated by a current divided from the TBGVCO to the DSVCO's center frequency. PA1 c. In the fine adjustment step, once the center frequency of the DSVCO is set, the reference clock is set to the data synchronizer's output in order to detect the appropriate synchronization pattern (14T/4T for DVD or 11T/11T for CD). Using the detection window and an up/down counter sets the DSVCO's frequency. The detection window identifies the next estimated synchronization pattern period (e.g., 1488T in a DVD-ROM's driver) and the up/down counter is used to fine adjust the DSVCO's frequency. PA1 lower data rates by using a current divider to the DSVCO. PA1 clock speeds no higher than the data read/write rate for the disk drive. PA1 a near capture-free Phase-Locked Loop (PLL) for a high-speed drive, in particular either CD or DVD drives. PA1 very fast seek time for reading from or writing to a data storage component. PA1 a very fast access time for reading from or writing to a data storage component. PA1 a more efficient method requiring less energy to implement. PA1 a time base generator (TBG) during wide capture operation. PA1 a synchronization detection "power down" mode to the entire circuit. PA1 an automatic power down enabled through a register control bit. PA1 detect output monitor pins synchronized through register control bits window detection accuracy synchronized through a register control bit. PA1 a T.sub.max counter read-only register for capturing the highest count. PA1 an up/down counter read-only register for capturing the count used in current scaling. PA1 a detect signal input to reset the data rate detection. PA1 two methods of current scaling, one for a wide capture range step and one for a fine adjustment step. PA1 application to any system using a PLL circuit. a capability of working without using a time base generator (TBG) PLL.
Conventional technology has required the T.sub.max pattern detection to occur at a clock rate of two to four times the read/write data rate. Assuming the clock's counter has a 2X-pattern detection rate, the count value variation would be 28.+-.2 (maximum) for the 14T DVD's drive. Further, the VCO synchronization clock would be programmed to 1/2 the clock counter's frequency. The capture range when in the phase detection mode of the PLL requires .+-.7% variation about the VCO's center frequency to accommodate variations in frequency due to the process itself, power supply voltage fluctuations, and temperature, among others. Because this assures the need for a kick pulse (the VCO's center frequency is continuously being adjusted) more power is dissipated because of the microprocessor's contribution to the adjustment and the need for continuous adjustment. When the conventional system is called on to perform this adjustment over very short time intervals, such as those associated with the new higher disk rotation speeds, it encounters physical limits to processing times. Therefore, there is a need for overcoming this limitation with a basic design change.